Heretofore protective coatings containing polytetrafluoroethylene resin have usually been applied to glass fibers or glass fiber fabrics where the glass fibers have not been sized or have had any sizing removed (ordinarily by heating to about 1100.degree. to 1300.degree. F. after weaving into fabric) or have been pre-coated only with a glass-resin coupling agent such as an organosilane.
Thus, Fluatt, Wong and Walsh have disclosed in their application entitled POLYTETRAFLUOROETHYLENE FLUOROCARBON RESIN-CONTAINING COATING COMPOSITION FOR GLASS FIBERS, Ser. No. 200,675, filed Oct. 27, 1980, the direct coating of virgin glass fibers with compositions containing polytetrafluoroethylene resin which are similar to those employed in the present invention for impregnating bundles of sized glass fibers.
U.S. Pat. No. 3,838,082 to Sauer discloses the use of aqueous dispersions consisting essentially of film-forming polytetrafluoroethylene and a polyhydrolyzable organosilane (including amine-functional silanes) or organic titanate, zirconate or tin compound, together with an anionic or nonionic surfactant and, optionally, a water-repellent such as a fluorinated acrylate polymer, for coating desized glass fiber fabrics. Sauer discloses the alternative use of the same compositions for coating "sized glass fabric," i.e., "griege goods." Sauer does not suggest the inclusion in his coating compositions of a second film-forming polymer or resin, other than the fluorinated acrylic polymers as optional water-repellents, and he presents data which indicates that other properties are sacrificed when such fluorinated acrylic water repellents are included.